On the basis of recent studies it has been shown that CFS sera contain antibodies to relatively insoluble cellular matrix antigens. Cellular structures (nuclear envelope, vimentin-containing intermediate filaments and a nuclear matrix particle visualized in immunofluorescence as reticulated speckles) associated with these antigens contain proteins that are part of the nuclear or cytoplasmic matrix. In collaboration with investigators at the University of Washington and at Harvard University, the PI and co-investigators at Scripps Research Institute will examine four research aims: 1) using previously collected blood samples from CFS patients from the two CFS center clinics and using currently developed assays the blood samples will be analyzed for the antibodies. They will be compared with patients with primary Sjogren's syndrome and primary fibromyalgia to determine whether differences in autoantibody specificities exist between different diseases and between CFS patients from different clinics; 2) ELISA assays will be developed for anti-lamin B1 and anti-vimentin using recombinant proteins expressed from cDNA clones, so that differences in antibody levels could be quantitated. This would be used in longitudinal studies of CFS patients to determine the role of humoral immunity in the natural history of the illness; 3) the possibility that there might be CFS-specific epitopes on lamin B1 and vimentin will be explored with expression products of PCR constructs, because if CFS-specific epitopes are detected, synthetic peptides of these regions could be used in highly specific immunological assays; 4) antibody screening of cDNA expression libraries will be performed to isolate the reticulated speckles nuclear antigen and a 45 kDa antigen. The antibody to the reticulated speckles could be a new or unique marker for CFS. The antibody to the 45 kDa antigen is present in Sjogren's syndrome but not in CFS-sicca and appears to be a distinguishing feature between the two clinical entities. Overall, these studies are aimed at rigorously defining autoantibody reactivities in CFS and may have etiologic implications.